Wasn't the picture taken in like November though, and not as part of a dedicated single photo shoot? I seem to remember people talking like they'd seen the picture before anyway when the cover was released...
And it obviously was going to be released anyway, since the Capitol insider leaked information that the track was being worked on by Katy and Luke in Novemeber/December, BUT I think Dressing Up was planned on being the first single until the divorce. Katy was talking about a saucy cat song that was coming out soon last March, and it was mastered about 3 months before Part of Me, so they obviously preferred it..
